Usefulness of Clinical Definitions of Influenza for Public Health Surveillance Purposes

Abstract

This study investigated the performance of various case definitions and influenza symptoms in a primary healthcare sentinel surveillance system. A retrospective study of the clinical and epidemiological characteristics of the cases reported by a primary healthcare sentinel surveillance network for eleven years in Catalonia was conducted. Crude and adjusted diagnostic odds ratios (aDORs) and 95% confidence intervals (CIs) of the case definitions and symptoms for all weeks and epidemic weeks were estimated. The most predictive case definition for laboratory-confirmed influenza was the World Health Organization (WHO) case definition for ILI in all weeks (aDOR 2.69; 95% CI 2.42-2.99) and epidemic weeks (aDOR 2.20; 95% CI 1.90-2.54). The symptoms that were significant positive predictors for confirmed influenza were fever, cough, myalgia, headache, malaise, and sudden onset. Fever had the highest aDOR in all weeks (4.03; 95% CI 3.38-4.80) and epidemic weeks (2.78; 95% CI 2.21-3.50). All of the case definitions assessed performed better in patients with comorbidities than in those without. The performance of symptoms varied by age groups, with fever being of high value in older people, and cough being of high value in children. In patients with comorbidities, the performance of fever was the highest (aDOR 5.45; 95% CI 3.43-8.66). No differences in the performance of the case definition or symptoms in influenza cases according to virus type were found.

Estimating the efficacy of symptom-based screening for COVID-19

“…These results suggest that, for both SARS-CoV-2 and other commonly diagnosed respiratory viral infections, the presenting symptoms at the time of the test order may not provide sufficient information to correctly classify whether a given patient will test positive for that virus. Prior studies of presenting symptoms and case definitions for influenza found that information on presenting symptoms alone is not sufficient to accurately diagnose influenza, or distinguish it from other influenza-like illnesses [8][9][10][11][12] , and our results support this finding. Though our Influenza Virus A model had one of the higher AUROCs we observed, it is not sufficient for use in a clinical setting.…”

Performance of suspected influenza case definition before and during the COVID-19 pandemic

“…No differences in the performance of the case definition or symptoms in influenza cases according to virus type were found in a recently published study [14]. The identified influenza virus sub-types were as following ( n = 7, 955): A/H1N1, 57%; B/Victoria, 17%; A/H3, 16%; B/Yamagata, 9% and B unidentified, 1%.…”

Applying symptom dynamics to accurately predict influenza virus infection: An international multicenter influenza‐like illness surveillance study

“…First, we modified the definition of influenza‐like illness in our eligibility criteria: fever and at least one of the three respiratory symptoms. Fever was deemed a powerful predictor of influenza virus infection in the past (OR: 3.47 to 4.03) 37,38 . However, Smith et al noted that patients with afebrile influenza virus infection had fewer respiratory symptoms 39 .…”